FG8. Near Earth Magnetosphere: plasma, fields, and coupling

Co-chairs:

• Sorin Zaharia (szaharia [at] lanl.gov)
• Stan Sazykin (sazykin [at] rice.edu) and
• Benoit Lavraud (Benoit.Lavraud [at] cesr.fr)

Group Overview

This focus group aims to improve physical knowledge and modeling of the near- Earth (< 10 RE) magnetosphere and its coupling with the outer magnetosphere. It broadens our understanding of inner magnetosphere plasma transport and includes the self-consistent coupling between plasma and electric and magnetic fields. It also focuses on quantifying the effect of plasma sheet source populations on the evolution of the inner magnetosphere.

Scientific Motivation

Currently there are gaps, in both modeling and observations, in our knowledge of both the fields and the plasma sheet boundary dependence. From a modeling point of view, a gap exists between self-consistent but physically oversimplified models and models that treat plasma correctly but not the fields. Existing global MHD models include self-consistent fields, but the MHD formalism cannot adequately describe the inner magnetosphere (closer than 10 RE), because it does not include gradient and curvature drifts. On the other hand, existing kinetic models (e.g. RAM, RCM, CRCM) treat plasma transport, acceleration and losses more or less realistically but do not properly account for the effect of the plasma on the fields. Observationally, the fields are also rather poorly described. While empirical models have been constructed that statistically describe B-fields and convective E-fields, they hardly do so for specific events; moreover, no model exists for the inductive E-fields. Finally, the dynamics of the inner magnetosphere depends both on the physics mechanisms involved, but also on the plasma sheet inputs. No clear study of the relative importance of the two exists. In summary, to further our knowledge of the inner magnetosphere we need better specification of the electric and magnetic fields, as well as of the driving plasma sheet properties. From a modeling point of view, it is desirable to have a kinetic approach that includes all relevant species (ions and electrons), self-consistent three-dimensional magnetic, convective and induced electric fields, as well as loss mechanisms.

Goals

This focus group will include both modeling and observational components that will improve the knowledge and specification of the inner magnetosphere electric and magnetic fields, their interaction with the plasma, as well as their dependence on the plasma sheet populations; a main deliverable will be the development of a realistic inner magnetosphere GGCM module, consistent with the main goal of the GEM program.

Potential Research Topics

1. Effect of the 3D self-consistent feedback between plasma and magnetic field on the inner magnetosphere particle transport and acceleration during various activity such as storms and substorms.
2. Specification (observational and modeling) of the convective E-field during storms, Region-2 field aligned currents, coupling to ionosphere and shielding.
3. Magnitude and location of the inductive E-fields arising from time-varying B-fields, through both modeling and observations (e.g. conjugate measurements – in situ plus ionospheric).
4. Effect of plasma sheet density, temperature and local time distribution on the large-scale morphology of the ring current ions and electrons in the inner magnetosphere.
5. Parameterization and relative importance of various loss processes during active times, including extreme disturbances.
6. Influence of inner magnetosphere fields on radiation belt particles; adiabatic effect; radial diffusion - what part, if any, of ULF wave diffusion is captured by time changing model fields?
7. Coupling of inner magnetosphere models with outer MHD models; which is driving which.

Original proposal to the GEM steering committee

Full text of the proposal to the GEM steering committee that led to creation of the focus group can be found here: PDF proposal

June 2008 GEM meeting report

The Near Earth Magnetosphere focus group held 3 breakout sessions in its 2nd year of activity at the 2008 GEM Summer Workshop in Zermatt, UT. The main goal of the focus group is to improve physical knowledge and modeling of near-Earth magnetosphere and its coupling with outer magnetosphere. The focus group is coordinated by Sorin Zaharia, Stan Sazykin and Benoit Lavraud.

The three focus group sessions, held on Tuesday and Wednesday (06/24-25) were well attended and featured short presentations and discussions of progress on the two main research fronts the focus group has concentrated to achieve its goals:

1. Data-based/empirical models - short presentations described both continuing progress on empirical modeling (such as the UNH IMEF E-field model), as well as a significant number of new research efforts on this front, from new magnetic field to plasma pressure models; below is a synopsis of the main topics discussed:

• Empirical plasma sheet specification – either for use in models (C. Lemon, a plasma sheet property database for geosynchronous orbit) or validating model results, e.g. observational verification of ring current injection from the plasma sheet (C.-P. Wang, Themis observations)
• Empirical E-field specification: overview of improvements in the UNH IMEF model based on Cluster data - the model is now publicly available (H. Matsui, P. Puhl-Quinn); its first use in a physics-based ring current model (V. Jordanova, RAM); dichotomy between convective electric field dependence on IMF southward turning in the plasma sheet vs. earthward of it (Y. Nishimura)
• Empirical B-field: M. Sitnov, new dynamical model (with a dramatic increase in spatial resolution); J. Zhang, T89GS - model constrained by spacecraft observations that satisfies force balance near spacecraft; R. Denton – adjusting TS05 model to better fit GOES observations; N. Ganushkina - event-oriented B-field model – modification of Tsyganenko model (good for studying detailed magnetic field variations for a specific event, time period, or magnetospheric region)
• Empirical plasma pressure model of the inner magnetosphere (P. Brandt – obtained by combining in-situ with global ENA observations)
• Radar observations of ionospheric convection (L. Lyons, Poker Flats AMISR; J. Baker, mid-latitude SuperDARN); qualitatively similar features observed in model results (Lyons, RCM)

2. The second research area, physics-based modeling, tackled mostly the coupling between different elements in the models (plasma, electric and magnetic fields); highlights from the presentations include:

• Modeling many events with simple setup (model works better for one storm type, i.e. sheath-driven storms, suggesting different storm drivers lead to more or less complex inner magnetosphere physics) (M. Liemohn, HEIDI - Michigan RAM)
• Ballooning instability in RCM-E; continued driving, simulating a growth phase, pushes the magnetosphere toward both MHD and fast MHD unstable states (F. Toffoletto)
• Substorm simulations: with RCM-E (J. Yang, using Geotail data to set up boundary; results consistent with observations); with a “bubble” imposed (RCM with new T89GS force-balanced model - J. Zhang; injection of bubble leads to higher pressure in the near-Earth magnetosphere)
• Wave studies: analytical pitch-angle diffusion - three lowest eigenvalues for the pitch-angle diffusion coefficient (M. Schulz; results could be used in ring current models); connection theory/observations - whistler modes (derived from LANL plasma observations + linear theory; enhanced growth rates found in the recovery phase; E. MacDonald)
• Effect of plasma boundary on RC injection (cold dense plasma more geoeffective; local time boundary distribution also very important - B. Lavraud, RAM; in simulations with self-consistent E-field, higher plasma sheet pressure causes quicker shielding of the penetration E-field - M. Gkioulidou, RCM)
• 1-way coupling of RAM with self-consistent B-field with SWMF (using SWMF pressure on RAM boundary) reconfirms previous results that cold, dense plasma sheet –a common feature in MHD models – is more “geoeffective,” i.e. leads to higher inner magnetosphere plasma pressure) (S. Zaharia)

The second half of the 3rd breakout session was devoted to a community discussion in which a future modeling challenge relevant to Focus Group goals emerged. The challenge will entail several near-Earth/inner magnetosphere models simulating, with same (or equivalent) input, both an idealized and a real event (geomagnetic storm). The challenge will bring together researchers from all major near-Earth magnetosphere modeling groups : RAM-SC B (LANL); HEIDI (Michigan RAM), RCM, RCM-E, CRCM, M. Chen’s model. The challenge will involve 3 stages: 1). Idealized event, with simple inputs/physics (with the goal of setting a baseline for all models). The second and third stage will involve full-physics modeling of an idealized and real event, respectively (thus the 3rd stage will involve both modelers and data analysts). More details about the challenge/model setup will be communicated to the community via e-mail and the new Focus Group Wiki. It is expected that the first stage be completed by and results presented at the 2008 GEM Mini-workshop (Sunday before AGU Meeting) in December, where the focus group plans to have a session. The 2009 Summer Workshop will then see initial results from the simulation of an idealized event with full model capabilities, with the goal of finding out the relative role of different physics features (e.g. plasma/fields self-consistency) present in the models.